body, html{
width:100%;
height:100%;
}
.imagen-fondo {
    position: relative;
    background: url('../imagenes/fondo.jpg') center no-repeat;
    background-size: cover;
    -webkit-background-size: cover;
    -moz-background-size: cover;
    -o-background-size: cover;
    width: 100%;
    height: 100%;
    text-align: center;
}


.imagen-fondo-pequeno {
    position: relative;
    background: url('../imagenes/fondo-pequeno.jpg') center no-repeat;
    background-size: cover;
    -webkit-background-size: cover;
    -moz-background-size: cover;
    -o-background-size: cover;
    width: 100%;
    height: 100%;
    text-align: center;
}